1. Field of the Invention
The present invention relates to a headlamp. More specifically, the invention relates to a headlamp which is advantageously used as a light source for an infrared night vision apparatus for a motor vehicle such as an automobile.
2. Description of the Related Art
In recent years, a safety technique that makes it easy to visually detect pedestrians and obstacles in the dark by means of an infrared night vision apparatus has been increasingly employed for enhancement of safety in driving an automobile at night.
Various types of automotive night vision apparatuses have been developed which, for example, include a so-called passive type and a so-called active type.
An automotive night vision apparatus of the passive type is configured such that far infrared radiation emitted from a pedestrian, an animal or the like is captured by an infrared camera for detecting the pedestrian, the animal or the like.
An automotive night vision apparatus of the active type is configured such that a pedestrian, an animal or the like present ahead is detected by projecting near infrared radiation forward, capturing reflection of the radiation by means of a camera, and displaying a captured image on a display device.
In the automotive night vision apparatus of the passive type, the infrared camera, which captures a very small amount of far infrared radiation emitted from the pedestrian, the animal or the like, is very expensive.
On the other hand, the automotive night vision apparatus of the active type, for example, utilizes the fact that light emitted from a bulb such as a halogen lamp contains near infrared radiation. That is, a high beam (also called “driving beam”) as well as a low beam (also called “pass-by beam”) are emitted from the headlamp, and only the near infrared radiation contained in the high beam is projected forward through a near infrared filter, and reflection of the near infrared radiation is captured by the camera.
There is also known an arrangement that includes a visible LED, a near infrared LED and a single reflection mirror for projecting visible light as well as near infrared light forward (see, for example, Japanese Unexamined Patent Publication No. 2004-241138).
However, where the bulb for the high beam projection is used as a near infrared light source, the high beam bulb is constantly turned on, disadvantageously leading to a significant increase in power consumption.
That is, the high beam bulb leads to the significant increase in the power consumption of the headlamp because the high beam bulb is turned on even during the projection of the low beam. At the same time, the high beam bulb suffers from a shorter service life and hence a shorter bulb change cycle because the high beam bulb is constantly turned on.
Where a light source for projection of the near infrared light is separately provided, an optical system including a lens and a reflection mirror is essentially required for projecting the near infrared light several tens of meters to 100 meters ahead. Provision of the dedicated optical system inevitably increases the size of the entire infrared night vision apparatus.
Where an optical system for either of the low beam or the high beams is doubled as the optical system for the near infrared light for prevention of the size increase of the apparatus, the low beam bulb or the high beam bulb is located at the focal point of the optical system to provide a proper light distribution pattern. Therefore, the optical system of the headlamp is disadvantageously complicated in order to project the near infrared light in a desired light distribution pattern.
The aforementioned arrangement including the visible LED, the near infrared LED and the single reflection mirror is capable of projecting the visible light and the near infrared light with lower power consumption. However, the visible LED and the near infrared LED should be positioned with respect to the single reflection mirror with a higher positioning accuracy in order to project the visible light and the near infrared light in desired light distribution patterns with the use of the single reflection mirror. Further, a strict limitation is imposed on positional relationships between the reflection mirror and the visible LED and between the reflection mirror and the near infrared LED.